With the development of the fifth generation wireless network to meet the demanding needs generated by artificial intelligence, augmented reality, virtual reality, autonomous driving, etc., reconfigurable optical add drop multiplexers are poised to penetrate into the edge access ring network, which was traditionally dominated by fixed optical add drop multiplexers. The key requirement for this emerging market is low cost.
A typical edge access ring network has less than ten nodes and two fiber rings handling east and west traffic. Wavelength selective switches are needed at each node for wavelength cross connect and add/drop, all controlled by software. FIG. 1A shows a possible configuration of such a system, wherein a pair of wavelength selective switches 10, 11 are used for a 2D reconfigurable optical add drop multiplexer node. For an M degree node (m-D node), m pairs of wavelength selective switches are used.
FIG. 1B shows the functionalities of a Reconfigurable Optical Add/Drop Multiplexer (ROADM) used in an optical node, which includes two separate wavelength selective switches 10 and 11, with one module for dropping different wavelength channels from COM_In port to different Drop ports and the Express_Out port, and one module for adding different channels from different Add ports and Express_In Port to the COM_Out port. Each module has its own switch engine to configure the channels to drop at drop ports 12A to 12N, and at add ports 13A to 13N. The Add module 10 and the Drop module 11 are often combined into a Twin module 14. The add or drop signal is processed by its own switch engine. This proliferation of switches adds cost and complexity to wavelength selective switches.